Md Jamal Uddin – Seminar/Ph.D. Preliminary Defense, Monday, November 14, 2016 at 1:00 P.M.
JSNN – Md Jamal Uddin – Ph.D. Preliminary Thesis Defense/Monday Seminar
Candidate: Md Jamal Uddin
Advisor: Sungjin Cho, Ph.D.
Date: Monday, November 14, 2016
Time: 1:00 P.M. – 3:00 P.M.
Location: JSNN Room 2092907 E. Gate City Blvd., Greensboro, NC 27401
Title: “Heterostructured Lithium Deficient Cathode Materials for Li-ion Batteries.”
A lithium deficient hetero-structured Lix(Ni1/3Mn1/3Co1/3)O2 (x<1.0) cathode material with multi-phase structure has been synthesized by sintering of metal hydroxide precursors with lithium carbonate. The metal hydroxide precursors were synthesized by a commercially common spray drying method, and the nanoscale morphology of the hydroxide precursors is translated to the synthesized cathode material during solid state sintering. The synthesized cathode material (hereafter denoted as MPS) were studied for their structure, morphology, and composition. The formation of a nanoscale, multi-phase, lithium deficient Lix(Ni1/3Mn1/3Co1/3)O2 cathode material was confirmed by scanning electron microscopy, energy dispersive spectroscopy, and inductively coupled plasma – optical emission spectroscopy. Synchrotron x-ray diffraction (SR-XRD) reveals the formation of layered structure (space group: R-3m) as well as a spinel structure (space group: Fd‑3m) in the MPS. In addition to that, SR-XRD also reveals the lattice parameter expansion of the R-3m phase in MPS which is likely due to the transition metal ion migration to the spinel phase during synthesis. High-resolution transmission electron microscopy and selective area electron diffraction data, from the cross section of the particle after focused ion beam milling, also confirmed the formation of spinel phase near the high cobalt areas, confirming the cation migration in spinel phase. With the structurally stable spinel phase in the material, MPS showed outstanding electrochemical performance compared to single phase commercial Lix(Ni1/3Mn1/3Co1/3)O2 (x>1.0, Umicore) material (hereafter denoted as SPS). MPS showed a capacity of 132.92 mAh/g at 1C (3.0 V – 4.5 V) retaining 75% of the initial capacity (177.67 mAh/g), compared to the SPS which showed 72% capacity retention. High-temperature cycling (60 °C, 1C/1C) up to 50 cycles revealed high capacity retention of 93.5% with MPS comparing to only 79.1% with SPS. The superior performance of MPS is attributed to the high voltage structural stability of the multi-phase structure.